1. Field of the Invention
The present invention relates to a liquid crystal display device. More particularly, the present invention relates to an array substrate for the liquid crystal display device having an integrated driving circuit and a method of fabricating the same.
2. Discussion of the Related Art
In general, a liquid crystal display (LCD) device uses the optical anisotropy and the polarization properties of liquid crystal molecules to display images. The LCD device includes first and second substrate facing each other and a liquid crystal layer interposed therebetween. The first substrate, referred to as an array substrate, includes a thin film transistor (TFT) that is used as a switching element. The second substrate, referred to as a color filter substrate, includes a color filter. The TFT includes a semiconductor layer made of amorphous silicon or polycrystalline silicon. Because a process using amorphous silicon is performed at a relatively low temperature and requires a relatively cheap insulating substrate, amorphous silicon has been widely used in TFTs. However, because the amorphous silicon has randomly arranged silicon atoms, a weak bonding strength between silicon atoms, dangling bonds and low field effect mobility occur in amorphous silicon. Accordingly, the TFT of the amorphous silicon is not adequate for a driving circuit (DC).
In contrast, because the polycrystalline silicon has an excellent field effect mobility, polycrystalline silicon is used for the TFT of the driving integrated circuit. Also, when the DC is formed on a substrate using polycrystalline silicon without using a tape automated bonding (TAB), an LCD device may become compact and the production cost of the LCD device may decrease.
FIG. 1 is a schematic plan view showing an array substrate for an LCD device according to the related art. As shown in FIG. 1, the first substrate 30 includes a display region D1 and a non-display region D2. A pixel region P, a TFT T on the pixel region P and a pixel electrode 17 connected to the TFT are formed in the display region D1. In addition, a gate line 12 along a first direction of the pixel region P and a data line 14 are formed to define the pixel region P. A gate DC 16 and a data DC 18 are formed on the non-display region D2 of the first substrate 30. The gate DC 16 and the data DC 18 supply a control signal and a data signal to the pixel region P through the gate line 12 and the data line 14, respectively. The gate DC 16 and the data DC 18 each has a TFT with a complementary metal-oxide semiconductor (CMOS) structure to output a suitable signal applied to the pixel region P. The TFT with the CMOS structure is used for rapidly treating signals in the driving integrated circuit. The CMOS structure includes n-type and p-type semiconductors.
FIG. 2 is a schematic plan view showing a display region of an LCD device having an integrated driving circuit on a first substrate according to the related art. As shown in FIG. 2, the display region of the first substrate 30 includes the gate line GL, the data line DL, the TFT T, the pixel electrode 70 and a storage capacitor Cst. The gate line GL and the data line DL cross each other to define the pixel region P, and the TFT T is formed at a crossing portion of the gate and data lines GL and DL. The pixel electrode 70 and the storage capacitor Cst are formed in the pixel region P. Because cross-talk is generated between the pixel electrode 70 and the gate line GL or the data line DL when the pixel electrode 70 overlaps the gate and data lines GL and DL, the quality of displayed images deteriorates. Thus, the pixel electrode 70 is spaced apart from the gate and data lines GL and DL. A black matrix 82 covers regions between the pixel electrode 70 and the gate and data lines GL and DL. The black matrix 82 also covers regions corresponding to the TFT T and the storage capacitor Cst.
FIG. 3A is a cross-sectional view showing a display region taken along the line III-III of FIG. 2 and FIG. 3B is a cross-sectional view showing a non-display region. A liquid crystal panel LP is shown. The first substrate 30 includes the TFT T, gate line GL, data line DL, and the pixel electrode 70. The TFT T may include a semiconductor layer 38, a gate electrode 52, a source electrode 72a and a drain electrode 72b. The TFT T may be formed by a process. First, a buffer layer 32 is formed on the first substrate 30. Then, the semiconductor layer 38 is formed on the buffer layer 32 by depositing, patterning and crystallizing amorphous silicon. A gate insulating layer 46 is deposited on the semiconductor layer 38. The gate electrode 52 and 54 are formed by depositing and patterning a conductive metal. Then, an interlayer insulating layer 60, the source and drain electrode 72a and 72b and a passivation layer 76 are sequentially formed. The pixel electrode 70 is formed on the passivation layer 76 to be connected to the drain electrode 72b through a drain contact hole of the passivation layer 76.
The second substrate 80 includes the black matrix 82, a color filter layer 84 and a common electrode 86. A liquid crystal layer LC is interposed between the first substrate 30 and the second substrate 80. The color filter layer 84 includes red, green and blue sub-color filters corresponding to the pixel region P. The common electrode 86 is formed on the color filter 84. The black matrix 82 is formed corresponding to the non-display region D2, the TFT T and the storage capacitor Cst. Also, the black matrix 82 covers the regions between the pixel electrode 70 and the gate line GL and the data line DL to block light passing through the regions. When the black matrix 82 is formed, a margin α that compensates for misalignment of the first substrate 30 and the second substrate 80 should be considered. Without the margin α, or a margin α and L, the quality of displayed images is deteriorated due to light leakage resulting from the misalignment of the first substrate 30 and the second substrate 80. Unfortunately, the margin causes the aperture ratio of the LCD device to decrease.
As shown in FIG. 3A, the DC is formed on the non-display region D2. The DC may include a CMOS structure including the n-type TFT T(n) of polycrystalline silicon and the p-type TFT T(p) of polycrystalline silicon. The TFT may be an n-type or a p-type TFT. The DC includes the TFTs T(n) and T(p) made of polycrystalline silicon having a CMOS structure. The TFTs T(n) and T(p) include the gate electrodes 48 and 50, the source electrodes 68a and 70a and the drain electrodes 68b and 70b. Because the gate insulating layer is formed as a thin layer on the semiconductor layer, the gate insulating layer has a step difference. Due to the step difference, the gate electrode can be disconnected in a crossing portion of the gate electrode and the semiconductor layer.
FIGS. 4A and 4B are enlarged perspective views showing the portion “F” of FIG. 2. As shown in FIGS. 4A and 4B, in the TFT T, the semiconductor layer 38 is formed on the first substrate 30 by depositing, patterning and crystallizing amorphous silicon. The semiconductor layer 38 is connected to the source and drain electrode 68a and 68b through first and second contact holes 66a and 66b. The gate insulating layer 46 is formed on the semiconductor layer 38, and then the gate electrode is formed on the gate insulating layer 46 by depositing and patterning conductive metal. The step difference of the gate insulating layer 38 affects the gate electrode 52. When the gate electrode 52 is formed using an etchant, the etchant pools into a crossing region G of the gate electrode 52 and the semiconductor layer 38 having the step difference. Accordingly, the gate electrode 52 is over etched to an extent that the gate electrode 52 becomes disconnected. Also, the process of fabricating the array substrate has many process steps. Thus, the process is disadvantageous.
FIGS. 5A to 5I and FIGS. 6A to 6I are cross-sectional views showing a process of fabricating a driving circuit and a pixel region in a display region according to the related art, respectively.
FIGS. 5A and 6A show a first mask process. As shown in FIGS. 5A and 6A, the display region D1 and the non-display region D2 are defined on the first substrate and the pixel region P is defined on the display region D1. In addition, first and second regions A1 and A2 are defined on the non-display region D2 and a switching region A3 and a storage region A4 are defined on the pixel region P.
First, the buffer layer 32 is formed on the first substrate 30 by depositing an insulating material. Then, first, second, third and fourth semiconductor layers 34, 36, 38 and 40 made of polycrystalline silicon may be formed on the buffer layer 32 in the first and second regions A1 and A2, the switching region A3 and the storage region A4 by depositing, patterning and crystallizing amorphous silicon. The first, second, third and fourth semiconductor layers 34, 36, 38 and 40 are patterned using a first patterning mask. The amorphous silicon may be crystallized using a laser. The first, second and third semiconductor layers 34, 36 and 38 function as an active layer. The fourth semiconductor layer 40 is a capacitor electrode, so the fourth semiconductor layer 40 is defined as a first storage electrode.
FIGS. 5B and 6B show a second mask process. As shown in FIGS. 5B and 6B, a photoresist is coated on entire surface of the first substrate 30 including the semiconductor layers 34, 36, 38 and 40. Then, a photoresist pattern 42 is formed to cover the first and second regions A1 and A2 and the switching region using a second patterning mask. The photoresist pattern 42 exposes the fourth semiconductor layer 40 in the storage region A4. Next, n-type or p-type ions are doped into the fourth semiconductor layer 40 using the photoresist pattern 42 as a doping mask. Because the fourth semiconductor layer 40 functions as a capacitor electrode 40, the n+ type impurities or p-type impurities are doped into the fourth semiconductor layer 40. The photoresist pattern 42 is removed from the first substrate 30.
FIGS. 5C and 6C show a third mask process. As shown in FIGS. 5C and 6C, a gate insulating layer 46 is formed on the entire surface of the first substrate 30 including the semiconductor layers 34, 36, 38 and 40 by depositing an inorganic insulating material. The inorganic insulating material may include silicon nitride and/or silicon oxide. Because the gate insulating layer 46 is formed on the semiconductor layers 34, 36, 38 and 40, the gate insulating layer 46 has a step difference. Next, first, second and third gate electrodes 48, 50 and 52 and a second storage electrode 54 are formed corresponding to the first, second, third and fourth gate electrodes 34, 36, 38 and 40, respectively, on the gate insulating layer 46 by depositing a conductive metal layer and patterning the conductive metal using a third patterning mask. The first, second and third gate electrodes 48, 50 and 52 have smaller sizes than the first, second and third semiconductor layers 34, 36 and 38, and the fourth gate electrode 54 has substantially the same size as the fourth semiconductor layer 40. Simultaneously, the gate line GL is formed in the switching region A3. The gate electrodes 48, 50 and 52 and the second storage electrode 54 are formed by wet etching the conductive metal layer using an etchant. Because the gate insulating layer 46 having the step difference affects the gate electrodes 48, 50 and 52 and the second storage electrode 54, the etchant pools into the crossing portion of the gate electrodes 48, 50 and 52 and the second storage electrode 54 and the semiconductor layers 34, 36, 38 and 40. Accordingly, the gate electrodes 48, 50 and 52 and the second storage electrode 54 are over etched to the extent that the gate electrodes 48, 50 and 52 and the second storage electrode 54 become disconnected.
FIGS. 5D and 6D show a process doping n+ type impurities into the semiconductor layer in the second region A2 and the switching region A3 using a fourth mask. As shown in FIGS. 5D and 6D, the photoresist is coated on the entire surface of the first substrate 30 and patterned using a fourth patterning mask to form the photoresist pattern 56 over the first region A1. The photoresist pattern 56 exposes the second, switching and storage regions A2, A3 and A4. Next, the n+ type impurities are doped into the second, switching and storage regions A2, A3 and A4. Consequently, the n+ type impurities are doped into both ends of the second and third semiconductor layers 36 and 38 using the second gate electrode 50 and the third gate electrode 52 as doping masks. Thus, both ends of the second and the third semiconductor layers 36 and 38 have ohmic contact characteristics. Both ends of the second and the third semiconductor layers 36 and 38 are thus defined as ohmic contact regions. The photoresist pattern 56 is then removed from the first substrate 30.
FIGS. 5E and 6E show a process doping p+ type impurities into the first region using a fifth mask. As shown in FIGS. 5E and 6E, a photoresist pattern 58 is formed on the first substrate 30 including the first, second and third gate electrode 48, 50 and 52 and the second storage electrode 54 by coating the photoresist layer and patterning the photoresist layer using the fifth patterning mask. The photoresist pattern 58 exposes the first region A1. Next, the p+ type impurities are doped into the first region A1 using the first gate electrode 78 as a doping mask. Consequently, the p+ type impurities are doped into both ends of the first semiconductor layer 34. Thus, both ends of the first semiconductor layer 34 have ohmic contact characteristics, as mentioned above. Both ends of the first semiconductor layer 34 are thus defined as ohmic contact regions.
FIGS. 5F and 6F show a sixth mask process. As shown in FIGS. 5F and 6F, an interlayer insulating layer 60 is formed on the entire surface of the first substrate 30 by depositing an inorganic insulating material such as silicon nitride and silicon oxide. Then, first contact holes 62a, 64a and 66a and second contact holes 62b, 64b and 66b are formed through the interlayer insulating layer 60 and the gate insulating layer 46 using a sixth patterning mask. The first contact holes 62a, 64a and 66a and second contact holes 62b, 64b and 66b expose the ohmic contact regions of the first, second and third semiconductor layer 34, 36 and 38.
FIGS. 5G and 6G show a seventh mask process. As shown in FIGS. 5G and 6G, source electrodes 68a, 70a and 72a and drain electrodes 68b, 70b and 72b are formed on the first substrate 30 by depositing a conductive metal layer and patterning the conductive metal layer using a seventh patterning mask. The source electrodes 68a, 70a and 72a are formed corresponding to the first, second and third semiconductor layers 34, 36 and 38, respectively, and contact respective ohmic contact regions of the first, second and third semiconductor layers 34, 36 and 38. Also, the drain electrodes 68b, 70b, 72b are formed corresponding to the first, second and third semiconductor layers 34, 36 and 38, respectively, and contact other ohmic contact regions of the first, second and third semiconductor layers 34, 36 and 38. The conductive metal may include chrome, molybdenum, tungsten, copper, aluminum alloy, etc. Simultaneously, a data line DL is formed on the display region D1. The data line DL is connected to the source electrodes 68a, 70a and 72a and crosses the gate line GL to define the pixel region P.
In the first through seventh mask processes, the CMOS structure including the n-type and p-type TFTs is formed in the non-display region D2. The n-type TFT is formed on the switching region A3 in the display region D1, and the storage capacitor Cst including the first and second storage electrode 40 and 54 is formed on the storage region A4 (Cst) in the display region D1.
FIGS. 5H and 6H show an eighth mask process. As shown in FIGS. 5H and 6H, a passivation layer 76 is formed on the entire surface of the first substrate 30 by depositing an insulating material such as silicon nitride and silicon oxide. Then, a drain contact hole 78 is formed through the passivation layer 76 to expose the drain electrode 72b in the switching region A3 by patterning the passivation layer 76 using an eighth patterning mask.
FIGS. 5I and 6I show a ninth mask process. A pixel electrode 70 is formed on the passivation layer 76 by depositing and patterning a transparent conductive metal using a ninth patterning mask. The pixel electrode 76 is formed on the pixel region P and contacts the drain electrode 72b through the drain contact hole 78. The transparent conductive metal may include indium-tin-oxide (ITO) or indium-zinc-oxide (IZO).
Through the above-mentioned processes, the array substrate according to the related art is formed.
Also, a color filter substrate may be formed through first to fourth mask processes. In the first mask process, the black matrix is formed on the second substrate. In the second, third and fourth mask process, the sub-color filters having red, green and blue colors, respectively, are formed corresponding to each pixel region. Then, the array substrate and the color filter substrate are attached to manufacture the LCD device.
As mentioned above, the LCD device according to the related art has several problems. For example, the gate electrode is disconnected at the crossing portion of the semiconductor layer and the gate electrode. Also, because the black matrix is lacking an appropriate margin, the LCD device has a low aperture ratio.